There is great interest in the rapid simultaneous detection of large numbers of biological species such as naturally occurring DNA, RNA, proteins, and other naturally occurring molecules, as well as man-made aptamers, synthetically modified proteins or toxins. Advances in biosensor technology have facilitated numerous potential medical applications, such as drug discovery, detecting genetic mutations and evaluating the effect of gene therapy or the identification of biological toxins.
For instance, traditional radio-immunoassay approaches to detecting proteins, hormones and various pathogens involve the binding of antibodies to a solid support to form a micro array and then exposing the analyte to the array of antibodies. The analysis of DNA fragments similarly involves fixing single stranded target DNA fragments, representing the genome of an organism, for example, to individual wells in a solid support to form a micro array. Such DNA micro arrays, also known as DNA chips, provide a highly sensitive means of detecting specific target DNA fragments. The micro array is analyzed by exposing target DNA fragments to fluorescently labeled probes of cDNA or mRNA of unknown identity. When the nucleic acid sequence of the probe cDNA or mRNA is complementary to the nucleic acid sequence of the target DNA, the probe cDNA or mRNA hybridizes to the DNA fragment. The flourescent label attached to the cDNA or mRNA is then detected with the aid of lasers and sensitive fluorescence detection equipment.
The wide-spread application of such DNA micro arrays and other types of arrays is limited by a number of factors, however. For example, the micro arrays and the fluorescently labeled cDNA and mRNA probes are expensive to produce or purchase. The high cost of lasers to initiate fluorescence, detection equipment, such as confocal microscopes and flourescent light detection equipment, also limit wide-spread applications of this technology. In addition, the shear bulk of such equipment limits the physical location where DNA micro arrays can be analyzed.
Electrical biosensor devices have been proposed as an alternative means for detecting DNA and RNA. An electrical readout corresponding to the concentration of a target molecule in a particular assay solution would allow a substantial reduction in the size and cost of the equipment needed to apply micro array technology. Previous biosensor devices have used an electrode comprising a semiconductive film made of organic polymers functionalized with selected species of probe oligonucleotides of single stranded nucleic acid sequences. Alternatively, monomers of the organic polymer are functionalized and then polymerized to form the functionalized organic polymer. In either case, the probe oligonucleotides are attached as side chains to the organic polymers. Semiconductive films are then made of the functionalized organic polymers. When exposed to a liquid containing the appropriate complementary target nucleic acid sequence, the probe and target nucleic acid sequence hybridize, thereby causing a detectable change in the conductivity of the functionalized organic polymers incorporated into the semiconductive film.
One objective of the invention is to provide sensitive electrical devices for the detection of a variety of target biological species. Another objective of the invention is to provide a method for the fabrication of such devices.